The present invention relates to a method for generating a frequency-modulated signal having improved receivability by a radio receiver.
More particularly, the present invention relates to a method for generating a frequency-modulated signal which is particularly useful in audio transmissions and even more particularly in stereo FM transmissions.
It is known that an input signal is transmitted by modulation performed in an FM modulator which frequency-modulates the input signal.
In practice, frequency modulation is achieved by varying the instantaneous frequency of the carrier as a function of the useful information.
In the radio receiver that is meant to receive the frequency-modulated signal there are provided suitable filters which suppress the side bands of the signal, which are generated according to Bessel""s theorem.
In practice, in the spectrum of an FM signal the first term of the spectrum represents the carrier, while the other terms represent the lateral components which are mutually spaced by the pulsing of the modulating wave and whose width is determined by Bessel functions.
The receiver section selects the signal to be received, filtering the received spectrum of the signal in a passband which is limited around a central frequency before frequency-demodulating the signal.
This filtering process inevitably removes some of the side bands of the received signals and this generates distortions of the signal obtained by frequency demodulation.
The aim of the present invention is to provide a method for generating a frequency-modulated signal whose receivability is higher in quality than known frequency-modulated signals.
Within the scope of this aim, an object of the present invention is to provide a method for generating a frequency-modulated signal in which the side bands are not eliminated in advance, as occurs with known frequency-modulated signals.
Another object of the present invention is to provide a method for generating a frequency-modulated signal which is suitable both for monophonic signals and for stereophonic signals.
Another object of the present invention is to provide a method for generating a frequency-modulated signal which is highly reliable, relatively easy to provide and at competitive costs.
This aim, these objects and others which will become apparent hereinafter are achieved by a method for generating a frequency-modulated signal with high receivability quality, comprising the steps of:
before sending an input modulating signal to a modulator, modifying said input modulating signal so as to compensate distortions which will be introduced in a modulated signal receiving section.